This invention relates to the measurement of hardness of a metal utilizing ultrasonic signals.
An existing method for measuring hardness in a metal is shown in U.S. Pat. No. 3,955,404 to Bickel, et al. The resonant frequency of a transducer is first measured. The transducer is then placed in contact with the subject metal. The new frequency of oscillation is measured and the difference between the frequencies is determined. A formula is then applied to this frequency difference to determine the hardness of the metal.
In practice, the hardness which is desired to be known is the average hardness of a metal. For any particular alloy (chemical composition) of a metal, several lattice structures are possible with varying amounts of hardness. When the metal is heated and annealed, an attempt is made to achieve a particular lattice structure, or crystalline structure, for that metal. The different structures are often referred to as phases of the metal. The hardness of the various phases or crystal structures is known, but the combination of phases in a particular metal resulting in a combination of hardness values is not known and is the average hardness value which is desired to be measured.